Rubber composition and method of preserving rubber



Patented June 11, 1940 UNITED STATES COMPOSITION AND Mn'rnon orPRESERVING RUBBER RUBBER PATENT OFFICE:

Raymond F. Dunbrook and Bingham J.

Humphrey, Akron, Ohio, assignors to The Firestone Tire & Rubber Company,Ohio, a corporation of Ohio Akron,

No Drawing. Application April 26, 1939,

Serial No. 270,206 r 15 Claims.

This invention relates especially to improved age-resisting rubbercompositions and methods of making the same, and is of primary utilityin the manufacture of carbon black rubber stocks,

such as tire tread stocks, that are subject to light, heat, oxidation,abrasion, flexing, and other destructive agencies during use. i

The chief objects of the invention are to provide a class of materialssuitable for incorporating i n, or for otherwise treating, rubber com-xpositions to retard deterioration thereof; to imwherein R in the 2 and 4lpositions is an alkyl radical and R. in the 6 position is an alkyl orcyclo-alkyl radical. I

It is known that 2,2,4-trimethyl-1,2-dihydroquinoline acts to someextent as an antioxidant for rubber. However, the relatively highvolatility of this substance has prevented it from being usedcommercially by the rubber industry. Some disadvantages which haveaccompanied the attempted utilization of this substance are thefollowing: (1) great loss of the substance by volatilization duringprocessing of the rubber mixtures, (2) danger to health of workmen dueto highconcentration of the vapor in the air during processing, and (3)excessive loss of the substance fromthe finished rubber article during.ordinary service, with consequent poor practical aging of the article.British Patent 450,323 describes a method of improving thetrimethyldihydroquinoline as an antioxidant by polymerizing it to anon-volatile resin.

Various substitution products of the trirnethyldihydroquinoline havebeen prepared and found to be much less volatile than the simplersubstance. However, the effectiveness of these new substances as rubberantioxidants varies greatly, some being much superior antioxidants tothe tri- 601 methyl-dihydroguinoline while others are entirelyinefiective in retarding rubber deterioration. It has now beendiscovered that consistently good results are obtained with compoundsfalling in the class of2,2,4-trialkyl-6-substituted-1,2-dihydroquinolines, wherein at least onealkyl group in the 2 position is a methyl radical and the groupsubstituted in the 6 position is an alkyl, Copending aparyl, alkoxyl oraroxylradical. plication, Serial No. 117,006, filed December 21, 1936,describes and claims the use in rubber of 2,2,4 trialkyl 6 aryl r 1,2dihydroquinolines, wherein at least one alkyl group in the 2 position isa methyl radical. The present application is a continuation in part ofcopending applications, Serial Nos. 89,654 and 117,004, filedrespectively on July 8, 1936, and December 21, 1936.

Such. dihydroquinolines substituted in the .6 position are unique amongthe substituted dihydroquinolines in respect tothe effect thereof inrubber. Said G-substituted' compounds are, in 0 general, considerablymore active as antioxidants than isomeric compounds substituted in the5, '7 or 8 positions. For instance, the G-phenyl compound is anexcellent antioxidant, whereas the B-phenyl compound is entirelyinefiective as a rubber antixoidant. Likewise, the 6-methyl substitutedcompoundis superior in laboratory tests to the unsubstituted simplecompound, 2,2,4-trimethyl-1,2-dihydroquinoline, whereas the 7- alkyl,cyclo-alkyl, aryl, alkoxyl or aroxyl group uniformly possess excellentantioxidant properties.

As illustrative examples of the preferred class of compounds, thefollowing specific embodiments of the compound are given:

(a) 2,2,4,6-tetramethyl-1,2-dihydroquinoline of 2,2,4-trimethyl-6butyl-LZ-dihydroquinoline of the formula (c)2,2,4-trimethyl-6-n-amyle1,2-dihydroquinoline of the formula (d)2,2,4-trimethyl-6-cyclo-heXy1 1,2-dihydroquinoline of the formula (e)2,2,4-trim'ethyl-G-tertiary-arny1-1,2 dihydroquinoline of the formulaThe. following are understood to be illustrative embodiments of theinvention and are not limzzitative of the scope thereof.

EXAMPLE 1 Control A 60 Parts by Parts 171 I weight weight Smoked sheetrubber 100 100 Sulfur n 3 3 5 l. 45 45 3 3 Stearic acid 3 3Mcrcaptobenzothiazole 1 1. 25 2,2,4,6-tetramethyl-1,2-dihydroquinoli 1The compositions were thoroughly mixed and then vulcanized underpressure for 120 minutes and 14.0 minutes at 264 F. Test strips were cutfrom the vulcanized stocks, some of said strips being artificially agedfor 46 hours in the Bierer- Davis oxygen bomb at 70 C. and 300poundsoxygen pressure. The results of physical tests 75 on these strips are asfollows:

, Normal data Modulus of elasticity in lbs./in. at iffigjg g gComposition 4Q0%e]ngat1n 5 Control .1 2250 2250 4650 4475 2150 2150 40004.450

After aging 46 hours in oxygen bomb Modplus Tensile strength in my atlbs/in. at break Composition 400% elongation I Control 1500 1300 1825,1425 EXAMPLE 2 Compounds b, c and (2 above, respectively 2,2,4-trimethyl6 butyl 1,2 dihydroquinoline,

2,2,4-trimethyl-6-n amyl-- 1,2 dihydroquinoline and 2,2,4-trimethyl-6cyclohexyl 1,2 dihyolroquinoline, were tested in a manner analogous tothat set forth in Example 1. The composition of the stocks was asfollows:

Control B C D Smoked sheet rubber l0 Slllf Stearic acid .1 Reactionproduct of mercapto- Eenzothiazole and formaldey 2, 2,4-trimethyl-6-butyl-1, 2-

dihydro uinoline n, 2, 2, 4-trimethyl-6-n-amyl-l, 2-

dihydroquinoline 2, 2, i-trimethy16cyclohexyl-1,

2-dihydro quinoline *U. S. Patent No. 1,960,197.

The resulting stocks were vulcanized for 120 minutes and 140 minutes at264? F. The results of physical tests onthese stocks are as follows:-

Normal data Modulus of elas- I ticity 1n lbs/in. Tensile strength in hat 400% elonga lbs/in. at break Composition tion o e 7 After agmg 46hours m oxygen bomb Modulus of elasticity in lbs/in. Tensile strength inat 400% elongalbs/in. at break Composition tion I Example 3 Compound (e)above, 2,2,4-trimethyl- 0-terti ar y-amyl-1,2-dihydroquinoline, wastested in a 7 Composition manner analogous-to that set forthin Example1.

The composition of the stocks was as follows:

Control E CI! p ragon-woo Di-ortho-tolyI-guanidine 2,4-trimethyl-6-tertiery-amyl-l, 2-dihydroquin- 1 The resulting stockswerevulcanized 'for 60, 85

and 120 minutes at 290 F. The results of physical tests on these stocksare as follows:

Normal data Modulus of elasticity in lbs/in! at 400% elongation Tensilestrength in lbs/in. at break Afitar aging 46 hours in oxygen bombModulus of elasticity in lbs/1'11. at 400% elongation Tensile strengthin lbs/i113 at break Composition 1'20 c0 st 120 The foregoing dataclearly. show that the various stocks treated with the improvedantioxidants compare {favorably with untreated stock in normalcondition, and after artificial aging, uniformly show superior 'modulusand tensile characteristics. Qualitative tests were made on a machinedescribed by L. V. Cooper, Analytical Edition of Industrial andEngineering Chemistry,

volume 2, pages 391-394, 1930. Compositions K, B, C, D and E, containingthe improved antioxidants were markedly superior in flex-crackingresistance to the respective control compositions. While the above datacoveronly specific compounds of the preferred class all members of saidclass are advantageous in carrying out the objects of the invention.Though the processes and products defined in the claims are primarilyuseful in connection with vulcanized rubber, they are i also effectivein improving the aging qualities of unvulcanized rubber, for example,rubberlatex compounds and unvulcanized rubber compounds for tire repairpurposes.

Modification may be resorted to, and the exact proportions of theconstituent materials may be varied, since the invention is not to belimited to the specific examples disclosed.

Whatisclaimed is: 1. A method of retarding the deterioration of rubberwhich comprises treating rubber with a 1,2-dihydroquinoline of thegeneral formula I i I H H wherein R. is an alkyl radical andR is amember of the group consisting of alkyl and cycloalkyl radicals.

2. The method of improving the properties of rubber which comprisesvulcanizing the rubber in the presence of a 1,2-dihydroquinoline of thegeneral formula wherein R is an alkyl radical and R is a member of thegroup consisting of alkyl and cycIo-alkyl radicals.

3. The method of retarding the deterioration of rubber which comprisestreating rubber with a 1,2-dihydroquinoline having alkyl groups in thea. and 6 positions and two alkyl groups in the 2 position, at least oneof which is methyl.

4. The method of improving the properties of rubber which comprisesvulcanizing rubber in the presence of a 1,2-dihydroquinoline of thegeneral formula it C wherein R is an alkyl radical. i

5. The method of retarding the deterioration of rubber which comprisestreating rubber with 2,2,4,6-tetramethy1-1,2-dihydroquinoline.

6. The method of improving the properties of rubber which comprisesvulcanizing rubber in the presence of2,2,4,6-tetramethy1-1,2-dihydrorubber which comprises vulcanizing rubberin the presence of 2,2,4-trimethyl-6-cyc1ohexy1-1,2- dihydroquinoline.

11. A rubber composition comprising a 1,2- dihydroquinoline of thegeneral formula wherein R. is an alkyl radical .and His a member of thegroup consisting of alkyl and cycloalkyl radicals.

12. A rubber composition comprising 9, 1,2- dihydroquinoline havingalkyl groups in the 4 and 6 positions and two alkyl groups in the-2position, at least one of which is methyl.

' 13. A rubber composition comprising 2,2,4,6-

l-iL'A rubber oomposition -comprising 2,2,4-trimethyl-6vbuty1-1;2adihyd1ioquino1ine. 15. A rubber compositioncomprising 2,2,4- trimethyl-6-cyclohexyl-1,2-dihydroquinoline.

RAYMOND F. DUNBROOK. BINGHAM J. HUMPHREY.

